The present invention relates to the making of hollows having rotational symmetry, particularly tubes, sleeves, or the like, and under utilization of molten atomized metal, either a pure metal or an alloy, by spraying the droplets of atomized metal onto a cylindrical capturing and shaping surface, while a relative motion in peripheral direction is introduced as between the spray and fog like state of the atomized metal, and the cyclindrical capturing surface.
A method of the type referred to above, particularly for making tubes, sleeves, or the like, is known, generally, and includes particularly the spraying of a fog of atomized molten metal onto a cylindrical capturing surface. A relative motion in peripheral direction, as far as the hollow to be made is concerned, is continuously provided. The capturing surface is specifically a round mandrel which is journalled at both end while rotating about its longitudinal axes. This way, then, a tube can be made by spraying the molten metal onto the rotating mandrel surface. Of course, the mandrel must be at least as long as the hollow to be made. In case the spraying beam is not as wide as the length of the hollow to be made, it is necessary to superimpose a longitudinal or axial motion upon the rotation of the mandrel. The length of the path for moving the mandrel in axial direction will then correspond to the length of the hollow to be made. On the other hand, if several spray heads are used, then the length of the longitudinal motion of the mandrel depends on the distance and spacing between the spray heads.
The hollow made by spraying metal droplets onto a mandrel serving as a capturing surface, can presently be made at a length of up to about 8 meters. Following the spray-on, i.e. upon completion of the tube making proper in that fashion, this tube has to be removed from a mandrel which, of course, has to be somewhat larger than 8 meters. This removal requires a rather extensive and expensive structure device. Moreover, another disadvantage of this method is simply to be seen in the fact that the mandrel has to be so long. Also, the mandrel would have to be heated prior to each spray step which, of course, requires further equipment and, in effect, wastes a large amount of energy.
Another drawback of the known method and equipment is that the rotation of the mandrel requires a high degree of accuracy, because one has to avoid that the mandrel looses its straightness. Finally, in spite of all these various aspects, there is an overall length limitation for making such a hollow because the longer the mandrel is, the higher will be the cost and complexity of the equipment involved in a disproportionate fashion.